I'm guessing that if US pulls their support, EU will try to add as much to cover up for it as humanly possible, as most compatriots see Ukraine as the frontline of something that can grow much, much bigger which because of remembering history, we'd obviously like to avoid.
The Patriot system is one the of best examples. EU doesn't really have anything in this space, but Ukraine needs more of it yesterday.
Are you talking about SAM capabilities or something else? Because there are plenty of SAMs produced by European countries; https://en.wikipedia.org/wiki/List_of_surface-to-air_missile...
This has turned out to be a major problem, as the US has used their re-export restrictions on components to block very significant parts of planned European military aid to Ukraine.
I speculate that there will be (already is) some extremely heavy investments in military tech R&D to remove/reduce dependence on American components going forward. As a continent, we can't have our hands tied like this in future conflicts.